The present invention relates to a gauging head suitable for coupling to a support for the linear dimension checking of a mechanical piece, comprising a shaped element defining a first reference portion, a second portion, or arm, movable with respect to the first, and an intermediate portion, or fulcrum, between the first and the second portion, that defines a geometric axis of reciprocal rotation between said first and second portion, a feeler fixed to said arm for contacting the piece to be checked, and a transducer device for providing signals responsive to the position of the feeler with respect to the reference portion, including two reciprocally movable parts, a first part thereof being stationary with respect to said first portion of the shaped element, and a second part being movable, together with said arm, with respect to the first portion.
The invention also relates to a checking apparatus for the linear dimension checking of a mechanical piece, comprising a support, a gauging head with a shaped element defining a first reference portion, stationary with respect to the support, a second portion, or arm, movable with respect to the first, and an intermediate portion, or fulcrum, between the first and the second portion, that defines an axis of reciprocal rotation between said first and second portion, a feeler fixed to said arm for contacting the piece to be checked, and a transducer device for providing signals responsive to the position of the feeler with respect to the reference portion, including two reciprocally movable parts, a first part thereof being stationary with respect to the first portion of the shaped element, and a second part being movable, together with said arm, with respect to the first portion, and a processing unit, electrically connected to the transducer device.
Furthermore, the invention relates to a process for machining the armset of a gauging, or measuring, head including an integral element that defines two reciprocally movable portions and a fulcrum between said portions.
There are known gauging heads for the geometric inspection of mechanical pieces that comprise a measuring arm with a feeler for contacting a piece to be checked, an element for supporting the arm, a fulcrum for allowing displacements of the arm with respect to the support element and a transducer for providing a signal responsive to the position of the arm with respect to the support element, in which the measuring arm, the support element and the fulcrum are formed from a single piece.
An example is provided in U.S. Pat. No. 4,409,737, that discloses gauging heads in which the support element comprises a wing, that extends in a direction perpendicular to the arm and enables the coupling -by means of screws- of the head to an external support. This type of coupling is quite lacking in versatility, in that, as the nominal dimensions of the piece to be checked vary, generally there is the need to replace the feeler and/or couple by means of screws the head in another area of the support or to another external support. In order to guarantee the correct operation of the head, the coupling existing between the wing and the external support must be extremely accurate. This involves precision mechanical machinings of the surfaces intended to be arranged into mutual contact for defining the position of the head, and particular care in coupling the head to the external support.
Moreover, in the measuring heads disclosed in the US patent, the arrangement of the fulcrum, feeler and transducer is such that the feeler displacements occurring further to contact with the surface of the piece to be checked and the displacements among the reciprocally movable parts of the transducer substantially occur along two parallel straight lines, but at a certain distance from each other. Consequently, the entity of the displacement of the elements of the transducer differs from that of the corresponding displacement of the feeler and, in order to process the correct detecting, it is necessary to keep into account the so-called xe2x80x9carms-ratioxe2x80x9d, i.e. the ratio existing between the distance separating the transducer and the feeler from the axis of rotation defined by the fulcrum. It is understood how undesired displacements in the position of the axis of rotation of the arm (due to a not entirely accurate implementing of the integral fulcrum) and/or flexions of the arm may negatively affect the operation of the head, modify the ratio between the feeler and the transducer displacements with respect to the theoretical condition that considers an xe2x80x9carm ratioxe2x80x9d evaluated on the basis of the head geometry.
The type of material utilized in the heads with armsets and so-called xe2x80x9cintegralxe2x80x9d fulcra normally undergoes a hardening process for the purpose of increasing its ultimate tensile stress and thus its resilient range. This process, apart from being expensive, is subject to other drawbacks. In fact, when the material is ground for thinning it at the point where it is desired to achieve the fulcrum, especially if it is desired to attain a very thin fulcrum, there is the risk that the material may considerably heat up at the thinned point, and thus loose the effects that the hardening process had provided. The materials utilized for hardening must contain carbon and, owing to the fact that they are consequently oxidable, need a final treatment, like, for example, zinc plating.
It is absolutely necessary to employ particularly yielding, and thus very thin, fulcra when it is required to check pieces having limited stiffness that could deflect under a high measuring force, or pieces made of a soft material, that could get scratched.
Because of the need to accomplish precision mechanical machinings, hardening, grinding and subsequent antioxidant treatment, it is evident that these gauges are expensive and it is often difficult to attain particularly thin and yielding fulcra.
An object of the present invention is to provide an extremely accurate, versatile, simple to manufacture and inexpensive gauging head that overcomes the limitations of the known gauging heads.
It is another object of the invention to provide a gauging head that has a measuring force low enough to permit its use even for checking resilient pieces.
These and other objects are achieved by a gauging head comprising a shaped element including a first reference portion, a second arm portion movable with respect to the first reference portion, and an intermediate portion, or fulcrum, between the reference and arm portion, that defines a geometric axis of reciprocal rotation between said reference and arm portion, a feeler fixed to said arm portion for contacting the piece to be checked, and a transducer device for providing signals responsive to the position of the feeler with respect to the reference portion, including two reciprocally movable parts, a first part thereof being stationary with respect to said reference portion of the shaped element, and a second part being movable, together with said arm portion, with respect to the reference portion, wherein the first part of the transducer device comprises a casing having an elongate shape, locked to the reference portion and including a coupling surface, said casing being adapted for locking to the support at said coupling surface for defining the position of the gauging head with respect to the support.
Yet another object of the present invention is to provide a checking apparatus for checking the linear dimensions of mechanical pieces that, apart from guaranteeing considerable accuracy, is extremely simple and can rapidly and easily be adapted for checking pieces that have different nominal dimensions.
This and other objects are achieved by an apparatus comprising a support, a gauging head with a shaped element for defining a first reference portion, stationary with respect to the support, a second arm portion movable with respect to the first reference portion, and an intermediate portion, or fulcrum, between the reference and arm portion, that defines a geometric axis of reciprocal rotation between said reference and arm portion, a feeler fixed to said arm portion for contacting the piece to be checked, and a transducer device for providing signals responsive to the position of the feeler with respect to the reference portion, including two reciprocally movable parts, a first part thereof being stationary with respect to said reference portion of the shaped element, and a second part being movable, together with said arm portion, with respect to the reference portion, and a processing unit, electrically connected to the transducer device of the gauging head, wherein the first part of the transducer device comprises a casing with an elongate shape, and the support comprises an opening and a locking/unlocking device for housing said casing and adjusting the position of the gauging head with respect to the support.
A considerable advantage that a gauging head and a checking apparatus according to the invention provide is the utmost flexibility, that enables to employ as transducer devices, both known gauges of various types (axial-sliding or xe2x80x9ccartridgexe2x80x9d heads, dial type comparators, or others) , and plain transducers (for example, Linear Variable Displacement Transducers, i.e. xe2x80x9cLVDTxe2x80x9d transducers) with windings and a ferromagnetic core coupled to the reciprocally movable parts of the armset, respectively. In this second case, an additional advantage that the heads according to the invention (and the apparatuses utilizing these heads) provide, is the friction free operation of the various moving, component parts.
An additional object that the invention provides is the attaining of an armset employed in gauging (or measuring) heads, that is extremely simple from a structural point of view, and can be manufactured by equally simple, rapid and economically convenient machinings.
This and other objects and advantages are achieved by a process including the steps of arranging a bar of metal material, and implementing a work hardening and a simultaneous reduction of the thickness of at least one area of the bar by compressing the area by means of a tool, thereby achieving a fulcrum and defining reciprocally movable portions.